thompson jj - electricity and matter

ELECTRICITY AND MATTER " J. J. THOMSON, D.Sc., LL.D., PH.D., F.R.S. ""FELLOW OF TRINITY COLLEGE, CAMBRIDGE; CAVENDISH PROFESSOR OF EXPERIMENTAL PHYSICS, CAMBRIDGE WITH DIAGRAMS NEW YORK CHARLES SCRIBNER'S SONS 1904 ÆTHERFORCE COPYRIGHT, 1904 BY YALE UNIVERSITY Published, March, 1904 ÆTHERFORCE THE SILLIMAN FOUNDATION. In the year 1883 a legacy of eighty thousand dollars was left to the President and Fellows of Yale College in the city of New Haven, to be held in trust, as a gift from her children, in memory of their beloved and honored mother Mrs. Hepsa Ely Silliinan. On this foundation Yale College was requested and directed to establish an annual course of lectures de- signed to illustrate the presence and providence, the wisdom and goodness of God, as manifested in the natural and moral world. These were to be designated as the Mrs. Hepsa Ely Silliinan Memorial Lectures. It was the belief of the testator that any orderly presenta- tion of the facts of nature or history contributed to the end of this foundation more effectively than any attempt to emphasize the elements of doctrine or of creed; and he therefore provided that lectures on dog- matic or polemical theology should be excluded from the scope of this foundation, and that the subjects should be selected rather from the domains of natural science and history, giving special prominence to astronomy, chemistry, geology, and anatomy. It was further directed that each annual course should be made the basis of a volume to form part of a series constituting a memorial to Mrs. Sillimau. The memo- rial fund came into the possession of the Corporation of Yale University in the year 1902; and the present volume constitutes the first of the series of memorial lectures. ÆTHERFORCE PREFACE In these Lectures given at Yale University in May, 1903, I have attempted to discuss the bear- ing of the recent advances made in Electrical Science on our views of the Constitution of Matter and the Nature of Electricity; two questions which are probably so intimately connected, that the solution of the one would supply that of the other. A characteristic feature of recent Electri- cal Researches, such as the study and discovery of Cathode and Rontgen Rays and Radio-active Substances, has been the very especial degree in which they have involved the relation between Matter and Electricity. In choosing a subject for the Silliman Lectures, it seemed to me that a consideration of the bear- ing of recent work on this relationship might be suitable, especially as such a discussion suggests multitudes of questions which would furnish ad- mirable subjects for further investigation by some of my hearers. Cambridge, Aug., 1903. J. J. THOMSON. ÆTHERFORCE CONTENTS CHAPTER- I CHE ELECTRIC OF FORCE 1 PAGE REPRESENTATION OF THE ELECTRIC FIELD BY LINES CHAPTER II ELECTRICAL AND BOUND MASS 30 CHAPTER III EFFECTS DUE TO THE ACCELERATION OF FARADAY TUBES 68 CHAPTER IV THE ATOMIC STRUCTURE OF ELECTRICITY 71 CHAPTER V THK CONSTITUTION OF THE ATOM 90 CHAPTER VI llAUIO-ACTIVITY AND RADIO-ACTIVE SUBSTANCES . . 140 ÆTHERFORCE ELECTRICITY AND MATTER CHAPTER I REPRESENTATION OF THE ELECTRIC FIELD BY LINES OF FORCE MY object in these lectures is to put before you in as simple and untechnical a manner as I can some views as to the nature of electricity, of the processes going on in the electric field, and of the connection between electrical and ordinary matter which have been suggested by the results of recent investigations. The progress of electrical science has been greatly promoted by speculations as to the nature of electricity. Indeed, it is hardly possible to overestimate the services rendered by two theories as old almost as the science itself ; I mean the theories known as the two- and the one-fluid theories of electricity. The two-fluid theory explains the phenomena of electro-statics by supposing that in the universe there are two fluids, uncreatable and indestruc- ÆTHERFORCE 2 ELECTRICITY AND MATTER tible, whose presence gives rise to electrical effects; one of these fluids is called positive, the other negative electricity, and electrical phenomena are explained by ascribing to the fluids the fol- lowing properties. The particles of the positive fluid repel each other with forces varying inversely as the square of the distance between them, as do also the particles of the negative fluid; on the other hand, the particles of the positive fluid at- tract those of the negative fluid. The attraction between two charges, m and m, of opposite signs are in one form of the theory supposed to be exactly equal to the repulsion between two charges, m and m of the same sign, placed in the same position as the previous charges. In an- other development of the theory the attraction is supposed to slightly exceed the repulsion, so as to afford a basis for the explanation of gravitation. The fluids are supposed to be exceedingly mo- bile and able to pass with great ease through con- ductors. The state of electrification of a body is determined by the difference between the quanti- ties of the two electric fluids contained by it ; if it contains more positive fluid than negative it is positively electrified, if it contains equal quantities it is uncharged. Since the fluids are uncreatable ÆTHERFORCE LINES OF FORCE 3 and indestructible, the appearance of the positive fluid in one place must be accompanied by the departure of the same quantity from some other place, so that the production of electrification of one sign must always be accompanied by the pro- duction of an equal amount of electrification of the opposite sign. On this view, every body is supposed to con- sist of three things : ordinary matter, positive elec- tricity, negative electricity. The two latter are supposed to exert forces on themselves and on each other, but in the earlier form of the theory no action was contemplated between ordinary matter and the electric fluids ; it was not until a comparatively recent date that Helmholtz intro- duced the idea of a specific attraction between ordinary matter and the electric fluids. He did this to explain what is known as contact electricity, i.e., the electrical separation produced when two metals, say zinc and copper, are put in contact with each other, the zinc becoming positively, the copper negatively electrified. Helmholtz sup- posed that there are forces between ordinary mat- ter and the electric fluids varying for different kinds of matter, the attraction of zinc for positive electricity being greater than that of copper, so ÆTHERFORCE 4 ELECTRICITY AND MATTER that when these metals are put in contact the zinc robs the copper of some of its positive electricity. There is an indefiniteness about the two-fluid theory which may be illustrated by the considera- tion of an unelectriEed body. All that the two- fluid theory tells us about such a body is that it contains equal quantities of the two fluids. It gives no information about the amount of either; indeed, it implies that if equal quantities of the two are added to the body, the body will be unaltered, equal quantities of the two fluids exactly neutraliz- ing each other. If we regard these fluids as being anything more substantial than the mathematical symbols + and this leads us into difficulties ; if we regard them as physical fluids, for example, we have to suppose that the mixture of the two fluids in equal proportions is something so devoid of physical properties that its existence has never been detected. The other fluid theory the one-fluid theory of Benjamin Franklin is not open to this objection. On this view there is only one electric fluid, the positive ; the part of the other is taken by ordi- nary matter, the particles of which are supposed to repel each other and attract the positive fluid, ÆTHERFORCE LINES OF FORCE 5 just as the particles of the negative fluid do on the two-fluid theory. Matter when unelectrified is supposed to be associated with just so much of the electric fluid that the attraction of the matter on a portion of the electric fluid outside it is just sufficient to counteract the repulsion exerted on the same fluid by the electric fluid associated with the matter. On this view, if the quantity of mat- ter in a body is known the quantity of electric fluid is at once determined. The services which the fluid theories have ren- dered to electricity are independent of the notion of a fluid with any physical properties ; the fluids were mathematical fictions, intended merely to give a local habitation to the attractions and repulsions existing between electrified bodies, and served as the means by which the splendid mathematical development of the theory of forces varying in- versely as the square of the distance which was inspired by the discovery of gravitation could be brought to bear on electrical phenomena. As long as we confine ourself to questions which only involve the law of forces between electrified bodies, and the simultaneous production of equal quantities of -{- and electricity, both theories must give the same results and there can be nothing to ÆTHERFORCE [...]... energy ; outside the -z od ; sphere, which as we have so that the whole kinetic seen is energy of the 2 m (2u -\ - the same as m 2u, 6 -f- o if -o- the \ ~~ i 0*, or the energy is mass of the sphere were 2 - instead of m a Thus, in consequence of ÆTHE ORCE RF ELECTRICITY 22 AND MATTKK the electric charge, the mass of the sphere 9,1 $ ~&^L^AAoL_ measured by -^ This is a very important is re- shows that part... the is and the number the difference between number passing through positively and the number passing through negatively For my own part, I have found the conception ÆTHE ORCE RF ELECTRICITY AND MATTER IQ of to much more readily Faraday tubes to lend itself the formation of a mental picture of the proc- esses going electric on in the than that of electric field for displacement, and have abandoned... those out- PQ] side and the line PQ will be bent outwards ÆTHE ORCE RF ELECTRICITY AND MATTER 12 Let us now pass from the case of two oppositely electrified bodies to that of two Let us suppose in Fig 3 electrified; since the A lines and of elec- similarly which are shown trified ones, the lines of force for B are positively force from start end on negatively electrified bodies, positively and will... bring before you as vividly and forcibly as I can, because the recognition of it makes the behavior of the electric field ÆTHE ORCE RF ELECTRICITY 24 AND MATTER to that entirely analogous of a mechanical sys- take an example, according to Newton's tem Third Law of Motion, Action and Reaction are To the equal and opposite, so that direction of Now, any momentum in any self-contained system is invariable... con- to produce a cur- flowing from the positively to the negatively charged plate through rent of electricity EF G we know, accompanied is, charged plate a magnetic force between the plates This by this ; magnetic force is as at right angles to the plane of the paper and equal to 47r the current in the plate, or, times the intensity of if a- is the density of the charge of electricity on the plates and. . .ELECTRICITY AND MATTER g decide between them who maticians Theories kind, " The physicists and mathe- did most to develop the "Fluid confined themselves to questions of this and refined and idealized the conception of these fluids until any reference to their physical properties not until was... physical realities Faramaterialized the lines of force and endowed day abstractions ÆTHE ORCE RF ELECTRICITY 1Q AND MATTER them with physical properties phenomena of the electric so as to explain the field Thus he sup- in a state of tension, and posed that they were Instead of an inthat repelled each other they at a distance between tangible action two electri- Faraday regarded the whole space between the... from an electrified point and a ÆTHE ORCE RF LINES OF FORCE 31 magnetic system, and the Vector Potential of that system, a quantity which plays a very large part in Maxwell's Theory of Electricity From the ex- we have given for the moment of momentum due to a charged point and a magnetic pole, we can at once find that due to a charge e of pression electricity at let a point P, and a little magnet the... greatest physicists have felt utterly unable to accept, and have devoted much thought and labor to replacing it by some- thing involving mechanical continuity Pre-eminent among them is Faraday Faraday was deeply influenced by the axiom, or if you prefer it, dogma where it is not Faraday, that matter cannot act who possessed, I believe, almost unrivalled mathe- matical insight, had had no training in analysis,... between the F FIG 5 originally in equilibrium under and the repulsion exerted by the tubes The repulsions due to those neighboring cut by G have now, however, disappeared so its tension, EF that PQ will no longer be in equilibrium, but will EFG be pushed towards tubes will be pushed into Thus, more and more E FG, and we shall ÆTHE ORCE RF ELECTRICITY jg AND MATTER have a movement of the whole set of tubes . electrified bodies, and the simultaneous production of equal quantities of -{ - and electricity, both theories must give the same results and there can be nothing to ÆTHERFORCE g ELECTRICITY AND MATTER decide between them. The physicists and mathe- maticians who did most to develop the "Fluid Theories " confined themselves to questions of this kind, and refined and idealized the conception of these fluids until any reference to. one-fluid theories of electricity. The two-fluid theory explains the phenomena of electro-statics by supposing that in the universe there are two fluids, uncreatable and indestruc- ÆTHERFORCE 2 ELECTRICITY AND MATTER tible, whose presence gives rise to. Electri- cal Researches, such as the study and discovery of Cathode and Rontgen Rays and Radio-active Substances, has been the very especial degree in which they have involved the relation between Matter and Electricity. In choosing a subject for the Silliman Lectures, it